This invention is a relatively wide-band electrically tunable reflector structure consisting of tandem Fabry-Perot resonators grown as a single epitaxial device.
Reflectance modulators are useful elements for bidirectional optical communication systems, for optical interconnection of integrated circuits in computer systems, and for optical logic applications. Optoelectronic devices incorporating epitaxially grown Fabry-Perot cavities are becoming increasingly important as reflectance modulators. For example, an electrically controlled reflectance modulator based on electro-optic effects in multiple quantum well (MQW) cavity structures has been described by Whitehead et al., Electronics Letters, Vol. 25, No. 9, Apr. 27, 1989, page 566, and Vol. 25, No. 15, Jul. 20, 1989, Page 984.
There are several characteristics that have limited the practical development of reflectance modulators. These characteristics include the highly precise control of layer thickness and composition required to attain operation at a given wavelength, and temperature dependences in the Fabry-Perot resonance and the MQW electro-optic properties that cause temperature variations of the optimum operating wavelength and of the contrast ratio.
While tandem resonators have been used to improve performance of optical bandpass filters by increasing their bandwidth for high transmission and their rejection outside the passband, H. Macleod, Thin-Film Optical Filters, (MacMillan, New York, 1986) Chapter 7, prior to this invention the use of tandem Fabry-Perot cavities for reflectance modulation has not been demonstrated. The invention recognizes the unique relationship of the reflections from the three mirrors that enables the tandem resonators to be used as a wideband modulator.